Reuse Size estimation endpoint for size/limit checking

[howardwkim]

• only in-situ observation datasets i.e. only datasets that fall within download thresholds

Todo

• tbl_dataset_stats - cache row numbers during initial call
• Temporal/spatial filtering should update the query_size column
• query_size - set and retrieved from backend on initial request + fallback value
• size check optimization - query count(lat) - dont get the whole dataset

[howardwkim]

Single dataset - don't apply limit since it might work -> no longer valid.

1. only in-situ observation datasets i.e. only datasets that fall within download thresholds
2. The UX will always include feedback about query size